1. Field of the Invention
The present invention relates to a technique for detecting the chip temperature of a power transistor, which drives a load such as an inductive load or a resistive load, quickly, at a low cost, and at high accuracy, so that it enables the entire system to operate safely.
2. Description of the Related Art
From the past, various protective circuits have been indispensable for the proper utilization of a power transistor, such as circuits for protection from excess electrical current and for protection from excess load (excess temperature) and the like. It is per se known to utilize a mirror transistor in which flows an electrical current which is proportional to the main electrical current as a current detection means for protection from excess electrical current, and it is per se known to use a chip temperature detection means for protection from excess load. As one example of a prior art chip temperature detection means, there is a per se known method of forming a diode in a polysilicon thin film upon the surface of the power transistor, and of detecting the temperature by taking advantage of the temperature dependence of the bias voltage when a fixed electric current flows in the forward direction through said polysilicon diode. This method has the beneficial point of being easy to apply, since such a polysilicon diode is perfectly separated from the power transistor by an dielectric material, and accordingly they do not mutually interfere with one another.
However, with a prior art technique such as the one described above, it is necessary to provide separate detection means for protecting against excess electrical current and excess load, in other words it is necessary to provide both the mirror transistor and also the polysilicon diode, and as a result the problem arises that the area which is occupied upon the power transistor chip becomes large.
Furthermore, with the above described prior art, as well as it being necessary to provide a mirror emitter (or source; hereinafter this will be referred to as the emitter) terminal for the mirror transistor, it is also necessary to provide two terminals for the polysilicon diode and it is moreover necessary to attach wires to these two terminals of the polysilicon diode. With a power transistor which is adapted to deal with a high electrical current, it is particularly necessary to attach emitter wires to the bonding pad as much and densely as possible, but with the construction described above there is the problem that it is not possible to attach emitter wires densely over the portion of the circumference of the chip where the polysilicon diode wires are present.
Yet further, if a current control type element which originally does not use polysilicon is used as the power element as described in Japanese Laid-Open Patent Publication H6-252408, it is needed to provide a temperature detection means such as the above described polysilicon diode or the like. As a result, a further process is entailed which is not required in the original semiconductor element manufacturing process, so that, along with the manufacturing cost being increased, the problem arises that a stepped portion is created upon the aluminum wiring above the temperature detection element and a bad influence is exerted upon the basic characteristics of the element itself.
Moreover, the symmetry of the original layout of an element is deteriorated by the presence of the region for temperature detection, and accordingly the problem regarding the layout also arises that a bad influence being exerted upon the characteristics of the element can not be avoided.
The present invention solves problems like the ones described above with prior art techniques, and provides an on-chip temperature detection device which is capable of performing speedy on-chip temperature detection at high accuracy, while not requiring the provision of any separate temperature detection means, thus preventing increase of the number of element manufacturing processes and enlargement of the chip area.
An on-chip temperature detection device according to the present invention, comprises: a bipolar type power transistor; a mirror transistor in which a collector current, which is proportional to a collector current of the power transistor, flows; a current detection section that detects the collector current of the mirror transistor; a voltage detection section that detects a voltage between a base and an emitter of the power transistor; and a calculation section that calculates a chip temperature of the power transistor, based upon the collector current of the mirror transistor detected by the current detection section, and upon the voltage between the base and the emitter of the power transistor detected by the voltage detection section.
Another on-chip temperature detection device according to the present invention, comprises: a bipolar type power transistor that is driven by a first drive signal; a voltage detection section that detects a voltage between a base and an emitter of the power transistor; a second drive signal generation circuit that generates a second drive signal which is a different signal from the first drive signal, and which drives the power transistor so that the voltage between the base and the emitter of the power transistor is less than a predetermined voltage; and a calculation section which calculates a chip temperature of the power transistor, when the power transistor is being driven by the second drive signal, based upon at least the voltage between the base and the emitter of the power transistor detected by the voltage detection section.
Another on-chip temperature detection device according to the present invention, comprises: a bipolar type power transistor that is driven by a first drive signal; a mirror transistor in which a collector current, which is proportional to a collector current of the power transistor, flows, when the power transistor is being driven by the first drive signal; a second drive signal generation circuit that generates a second drive signal which is a different signal from the first drive signal, which flows a predetermined current in the mirror transistor so that a voltage between a base and an emitter of the mirror transistor is less than a predetermined voltage, and which drives the power transistor to be OFF; a voltage detection section that detects the voltage between the base and the emitter of the mirror transistor; and a calculation section that calculates a chip temperature of the power transistor, when the mirror transistor and the power transistor are being driven by the second drive signal, based upon at least the voltage between the base and the emitter of the mirror transistor detected by the voltage detection section.
Another on-chip temperature detection device according to the present invention, comprises: a bipolar type power transistor that is driven by a first drive signal; a mirror transistor in which a collector current, which is proportional to the collector current of the power transistor, flows, when the power transistor is being driven by the first drive signal; an OFF signal generation circuit that generates an OFF signal which turns the power transistor OFF when the first drive signal is OFF; a current drive circuit that flows a predetermined current in the mirror transistor so that a voltage between a base and an emitter of the mirror transistor is less than a predetermined voltage, when the first drive signal is OFF and the power transistor is turned OFF by the OFF signal; a voltage detection section that detects the voltage between the base and the emitter of the mirror transistor; and a calculation section that calculates a chip temperature of the power transistor, when the first drive signal is OFF and the power transistor is turned OFF by the OFF signal, based upon at least the voltage between the base and the emitter of the mirror transistor detected by the voltage detection section.
Another on-chip temperature detection device according to the present invention, comprises: a power transistor that may be a bipolar type or a MOS type including an IGBT, having a collector or drain terminal, an emitter or source terminal, and a base or gate terminal; a mirror transistor having a collector or drain terminal and a base or gate terminal which are the same, respectively, as the collector or drain terminal and the base or gate terminal of the power transistor, and a mirror emitter or mirror source terminal which is independent from the emitter or source terminal of the power transistor; a control circuit that keeps a collector or drain current which flows in the mirror transistor constant; and a calculation section that flows a predetermined current in a collector or drain of the mirror transistor only while the power transistor is OFF, that measures the voltage between the base or gate terminal and the emitter or source terminal of the mirror transistor at this time, and that calculates the chip temperature of the power transistor based on a temperature characteristic of the voltage.
Another on-chip temperature detection device according to the present invention, comprises: a power transistor that supplies a current based upon a drive signal; a mirror transistor in which flows a current which is proportional to the current being supplied by and flowing in the power transistor; a current detection means for detecting the current flowing in the mirror transistor; a voltage detection means for detecting a voltage between a drive signal input terminal and a current supply terminal of the power transistor; and a calculation means for calculating a chip temperature of the power transistor, based upon at least one of the current detected by the current detection means and the voltage detected by the voltage detection means.